Nicotinic receptors play important physiological roles in the nervous system and are implicated both in nicotine addiction and various pathophysiological states. It is now clear that nicotinic receptors exist as a family of related gene products, but the functional significance of the individual receptor subtypes is not now known. The purpose of this proposal is to characterize neuronal nicotinic receptors as they exist in neural tissue, and to use probes developed in model nicotinic receptor systems to aid in our understanding of these receptors. One model system is genetically-defined nicotinic receptor subtypes expressed in Xenopus oocytes. A second model system is the chick retina that has high concentrations of functional nicotinic receptors, consisting of unknown receptor subtypes. Electrophysiological recording from functional nicotinic receptors in both of these model systems already have or will be used to determine pharmacological properties of receptor subtypes, particularly the affinity of the receptor subtypes for agonists. In addition, these model systems will be used to develop novel affinity alkylating and affinity redox agents for nicotinic receptors that will be used subsequently for labeling and identifying receptor subtypes. Using the oocyte system, snake venom neurotoxins that may discriminate between receptor subtypes will be screened for pharmacological activity. The interaction of an established snake venom neurotoxin, referred to as neuronal bungarotoxin, with the chick retina receptors will be investigated, with particular interest in the effects of detergent solubilization on the properties of these subtypes of nicotinic receptors. Using the chick retina as a model of a brain slice from laminated tissue, novel recording technique that evokes extracellular field potentials due to the selective activation of nicotinic receptors will be evaluated. Finally, to test the general applicability of this recording technique, the pharmacological and physiological properties of nicotinic receptors in chick optic tectum and rat superior colliculus will be investigated. The effects of snake toxins and affinity alkylating agents on these brain receptors will be studied. If possible, the properties of the receptor subtypes expressed in the chick retina and optic tectum and in the rat superior colliculus will be correlated with the subtypes as expressed in the Xenopus oocyte system.